From: Sonny Heath (sonny@defuniak.com)
Date: Thu Jun 29 2006 - 06:37:31 PDT
Bill,
If you had to take off the fuel supply pump it may be simpler to remove the
injector pump instead of jacking the engine up. Whatayathink?
Sonny
----- Original Message -----
> After last falls trail ride my truck sat all winter and spring awaiting
From: "Bill & Bonnie" <bprestin@chartermi.net>
To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
Sent: Thursday, June 29, 2006 12:25 AM
Subject: Re: [MV] M342 (M35A2)fuel delivery problem
> further attention. I was finally spurred to figure it out so as not to
> miss this years forth of July parade here in Birch Run, MI.
>
> You can read the previous message below this one to see what my engine
> problems were.
>
> The fuel system looks very complicated but is not too bad once it is
> understood.
>
> Here is how the system works:
> There is an in tank electric fuel boost pump that sends 5-7 lbs of
> fuel pressure through the frame mounted primary fuel filter housing to the
> fuel supply pump mounted on the side of the fuel injector pump. This fuel
> supply pump is gear driven from the injector pump and supplies fuel under
> pressure(30lbs at idle-75lbs at speed) depending on engine RPM to the
> engine mounted fuel filter housing.
> In the top of the engine mounted fuel filter housing is a pressure
> regulator valve that starts to open at approximately 60 lbs and regulates
> the engine fuel pressure between 65 and 75 lbs psi. at 2000 RPM and above.
> Any excess fuel allowed to escape by the opening of the fuel pressure
> regulating valve is sent back to the fuel tank. This 65-75 lbs.
> pressurized fuel is sent through the engine mounted secondary fuel filter
> housings and to the fuel density compensator mounted on top of the fuel
> injector pump. After passing through the fuel density compensator the fuel
> enters the fuel injector pumps hydraulic head and is pressurized to a high
> level and sent to the fuel injectors. Excess fuel returning from the fuel
> injectors and flame heater assy returns to the injector pump fuel overflow
> valve assy on top of the front of the fuel injector pump and is sent back
> to the fuel tank via the same fuel line coming from the fuel pressure
> regulator valve.
>
> I measured the pressure at the primary fuel filter and found I had the
> necessary 7lbs of pressure. I measured it at the top bleeder valve on the
> secondary fuel filter housings mounted on the engine and found 50lbs of
> pressure at 1200 RPM. This was within the specified 48-57lbs for that
> engine speed. I measured it after the secondary fuel filter housing but
> before it re-entered the injector pump and found the same 50lbs of
> pressure.
> Then a funny thing started to happen. As the engine warmed up(about 10
> min.of running) the 50 lbs of pressure dropped off to 28lbs. After really
> reading into the manuals I figured out the above system and thought it
> might be the fuel pressure regulating valve. If it was the fuel supply
> pump the engine would have to be jacked up to remove it from the side of
> the injector pump as there is less than one inch between the boost pump
> and the steering gear box. I am not sure the engine could be raised enough
> as there is only a couple of inches between the top of the flywheel bell
> housing and the cabs firewall.
> On top of the engine mounted secondary fuel filter housing there is
> what looks like an extra bolt, its really a plug with an O-ring. When I
> unscrewed it a spring flew out and almost got lost under the truck. I used
> a pair of needle nose pliers and pulled out the valve plunger and under it
> was a piece of crud holding it up off its seat. I cleaned the plunger and
> its seat and reinstalled the parts.
> After this I ran the engine for almost a half an hour at 1200 RPM. The
> pressure stayed above 50 lbs. at all times.
>
> I'll take it for a test drive tomorrow but I am sure it is fixed.
>
> Here are the pressures necessary at the top of the secondary fuel filter
> housing.
>
> RPM Min press lbs Max press lbs
> 700 30 35
> 1200 48 57
> 1600 57 64
> 2000 63 69
> 2400 65 73
> 2600& above65 75
>
>
> Bill
> Michigan
>
> ----- Original Message -----
> From: "Bill & Bonnie Prestin" <bprestin@chartermi.net>
> To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
> Sent: Sunday, October 09, 2005 4:03 AM
> Subject: [MV] M342 (M35A2)fuel delivery problem
>
>
>> Hi,
>> I have an M342 dump truck with an LDS465-1C engine, I am struggling
>> with fuel delivery problems. It will drive down the road great for a
>> couple of miles (accelerates fine) then just runs out of fuel. After
>> sitting for a few minutes with the fuel pump turned on, it will start
>> back up and drive a couple of miles more. It will also idle fine forever,
>> so a little fuel is getting through. I changed all the fuel filters,
>> still no luck. I also tried bleeding the valve above the fuel filters on
>> the engine while the truck is idling. Plenty of fuel squirts out, so the
>> problem must be beyond there. The problem developed while I was up in
>> northern Michigan on our clubs fall trail ride. The 120 mile trip home
>> was pretty rough.
>> Anyone have any ideas where the system might be clogged? My engine has
>> the sticker on the side that says
>> "use diesel fuel only. Fuel compensator has been bypassed to prevent
>> engine oil dilution"
>> But there is still a maze of fuel lines around the injector pump.
>>
>>
>>
>> Bill
>> Michigan
>>
>>
>>
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